In these later days, ceramics of varied types have come to be used in a variety of industrial fields. Of these ceramics, those which are destined for medical treatment are expected to find their uses in such a field as the manufacture of artificial bone or dental treatment. Such ceramics destined for medical treatment as used in the field of dental treatment include dental porcelain materials (hereinafter simply called porcelain in certain cases) which consist essentially of silica or alumina and further contain modified oxides for improving melting point, sintering characteristics, color tone, etc. This porcelain has been used for manufacturing porcelain tooth, porcelain baked crown, jacket crown, etc. and, in addition thereto, utility as artificial tooth of the porcelain has now been under investigation.
Dental treatment using such porcelain has heretofore been practiced, for example, by first making a metallic crown so as to fit a decayed tooth after removing by scraping the decayed portion therefrom, putting together by baking the porcelain and metallic crown to make a porcelain baked crown, and covering the tooth with the porcelain baked crown. In that case, however, there was involved such problem that the procelain used sometimes breaks into pieces because it is hard and brittle, or because of being poor in its adhesion to metal, the porcelain baked comes off from the metallic crown. Where the porcelain broke into pieces, in particular, there was brought about such problem that an expensive porcelain baked crown must be made anew because broken pieces of the porcelain cannot be strongly joined together.
With the view of solving such problems as referred to above, there have been proposed adhesives which are alleged to have adhesiveness to porcelain. For example, "The Journal of the Japanese Society for Dental Materials and Devices", Vol. 3, No. 6, 739-746, discloses adhesives which are believed to be adhesive to porcelain, said adhesives comprising (i) silane coupling agents, (ii) polymerizable monomers such as 4-methacryloxyethyltrimellitic acid anhydride (hereinafter called 4-META for short in certain cases), (iii) polymerizable monomers such as methyl methacrylate (hereinafter called MMA for short in certain cases) and (iv) polymerization catalysts such as tributylboron (hereinafter called TBB in certain cases).
Although the adhesives referred to above are excellent in adhesion properties to a certain extent in comparison with conventionally proposed adhesives for porcelain much reliance cannot be placed thereon as their adhesive strength greatly varies according to the condition under which they are used and, moreover, they are not sufficient enough in respect of water resistance, and accordingly they have been in great need of further improved adhesion properties.
Extensive researches conducted intensely by the present inventors with the purpose of solving the above-mentioned problems associated with the prior art and of obtaining adhesives for ceramics excellent in adhesion properties which do not vary according to the conditions under which they are used and, moreover, excellent in water resistance, have resulted in completion of the present invention on the basis of their finding that such purpose may well be attained by adding to conventionally known adhesives for ceramics (i) a specific first acidic compound or (ii) a metal salt, or (iii) a metal salt and a specific second acidic compound.